The present invention relates to a surgical knife for use in eye surgery and a method for performing a radial keratotomy (RK) surgical procedure. More particularly, the invention relates to a knife design and a method which allow corneal incisions in an RK procedure to be precisely enhanced by extending precisely and safely the incisions centripetally.
The RK surgical procedure is performed to correct myopia (nearsightedness). In a typical initial procedure, a surgeon uses a surgical knife to make four to eight (or more) spoke-like radial cuts of a controlled depth in the paracentral and peripheral cornea to produce a flattening effect on the central cornea. Exact extension of incisions into the optical zone of the cornea and a precise depth of cut are important so that the correction of curvature of the cornea is not too great or too little.
Since an RK procedure involves cutting the cornea of a human eye, great care must be taken to ensure that the cuts are precise and at the depth necessary to provide for the indicated correction. Consistent results are difficult to achieve. A problem which has been known to occur is an under-correction of the myopia through cuts which are not as deep or long as required. Cuts are normally made conservatively because the knife is extremely sharp and many surgeons tend to be overcautious when the knife is close to the optical zone, the uncut central portion of cornea.
Inevitably, a certain percentage of RK procedures performed are not entirely successful in that the curvature of the cornea has not been flattened enough. In such a situation, a first enhancement procedure may be performed with an enhancement blade that is sharp only near the point of the blade. The enhancement blade is used in one or more selected incisions to even out the bottoms of the incisions and to square off the ends of the incisions adjacent to the optical zone at the center of the cornea. Oftentimes, the first enhancement procedure is carried out during the original operation.
If additional enhancement is required, most surgeons extend the incisions centripetally toward the center of the cornea. At least two basic procedures for extending an incision are used. In the Russian (centripetal) technique, a surgical knife starts in the initial incision and extends toward the center of the cornea. The Russian technique has the advantage of greater attained depth and a squarer cut end, resulting in greater correction. However, the Russian technique has a considerable disadvantage in that there is a danger of extending the incision too far towards the center of the cornea. In the American (centrifugal) technique, alternatively, a new incision is started at the end of the new smaller optical zone and extending outwardly to connect with the original incision. The American technique has an advantage in that the danger of cutting into the optical zone of the cornea is eliminated. The American technique, too, has a considerable disadvantage in that the new incision tends to be shallower and may not lie in line with and interconnect to the end of the original incision. In such a case, vision may become obscured, and the overlapping, parallel incisions exacerbate glare.
It would be advantageous to combine the safety of the American technique with the greater precision of the Russian technique.